Process for separating niobium and tantalum from materials containing these metals



PROCESS FOR SEPARATING NIOBIUM AND TAN- TALUM FROM MATERIALS CONTAINING THESE METALS Waldemar Sclnornstein, Arlesheim, and Fritz Kern, Binningen, Switzerland, assignors to Ciba Limited, Basel, Switzerland, a Swiss firm No Drawing. Application February 24, 1956 Serial No. 567,475

Claims priority, application Switzerland March 1, 1955 7 Claims. (31. 23-18) It is known that the two chemically related metals tantalum and nioblum (also known in certain countries as columbium), which are generally found together in nature, are very difficult to separate from one another.

So far as is known, the method of separation is still substantially that of Marignac (1865). The method of Marignac involves the fractional crystallization of the alkali double fluorides, whereby the more sparingly soluble 'K TaF is separated from the solution containing The main disadvantage of this method is that it necessitates working with hydrofluoric acid.

The process described in French Patent No. 973,896, which involves the selective chlorination of materials which contain niobium and tantalum in oxidized form, is carried out in the absence of reducing gases but at very high temperatures (about 1200 C.). The method of separation by forming the nitrides followed by halogenation as describedin United States Patent Number 2,427,360, and also the process described in United States Patent Number 2,244,254 in which the niobium constituent is first selectively reduced at 600 1200" C. and then chlorinated, both necessitate twohigh temperature treatments.

The method of separation described in United States Patent No. 2,537,316 depends on the reduction of the accompanying elements in a more or less colloidal solution'or suspension obtained by the digestion of the ore with, for example, sulfuric acid, followed by selective,

hydrolysis, in which the reduced accompanying elements remain in solution. The method therefore uses very unstable solutions, and the digestion with sulfuric acid is a lengthy process.

Finally, it is very difficult to maintain the working conditions in the potassium oxalate hydrolysis described in United States Patent No. 2,481,584.

The present invention is based on the; observation that niobium and tantalum can be separated from one another in an advantageous manner by converting a material which contains niobium and tantalum in oxidized form,

t for example, a slag or more especially a concentrate or an ore, which may have been'treated to enrich the'concentration of these metals, or a mixture of oxides of these metals, by means of chlorine gas and a reducing agent into a chlorination mixture which contains the niobium preponderantly or exclusively in the form of its oxychloride and the tantalum in the form of its pentachloride, and separating the tantalum pentachloride from the said mixture by extraction with an inert solvent with theexclusion of moisture. t

As starting materials for the present process there may be used the ordinary mixtures available in industry which contain oxides of niobium and tantalum or natural products which contain these two elements mostly in the form of their oxides.

The chlorination mixtures, which contain the tantalum for the greater part in the form of its pentachloride (TaCl and the niobiumfor the greater part in the form of its oxychloride can be produced by methods in them- 2,842,424 PatentedJuly 8.,

or exclusively in the form of its pentachloride, it, is neces sary to avoid subsequent reaction of the chlorination products. Therefore, the vapours of the chlorination products must be allowed to remain at high temperature in contactwith one another and with the waste chlorination gases, which may contain carbon monoxide and chlorine, only for an extremely short time, that is to say, at most for a few seconds. 'This can be achieved for example, by dilution with other gases, for example, with returned chloride-free reaction gas, or by providing between the chlorination vessel and the condensera conduit.

which is very short or of very small cross-section.

Owing to the tendency of niobium to. form oxychlorides there can be obtained by these methods a chlorination mixture which containsthe niobium predominantly -or wholly in the form of oxychloride andythe tantalum pre dominantly or wholly in the form of its pentachloride.

The elements, other than niobium and tantalum, which are customarily presentin the form of compounds as impurities in the starting materials, and of which the chlorides are also formed during the; chlorination, for example, the chlorides of titanium, tin, manganese etc), can be separated in a simple manner, for example, by so adjusting the temperature in the chlorination vessel'and in the condenser that the chlorides "of the accompanying elements, whose boiling or volatilizing points are generally far removed from those of the chlorides of niobium and tantalum, are separated to a very great extent from the latter chlorides. Thus, for example, the less volatile chloride of magnanese may be separated first, While the more volatile chlorides, for, example, those of silicon,

tin and titanium,precipitate after the chlorination mixture containing niobium and tantalum has been con-,

densed, for example, in condensation zones of lower' temperature. t 3:

Mixtures of tantalum pentachloride and niobium oxychloride to be separated into their constituentsin accordance with the invention can also be obtained by a process of the kind referred to which is carried so far as to produce predominantly a mixture of niobium pentachloride and tantalum pentachloride followed by a selective hydrolysis, for example, by means of steam or oxidehydrates, or by the selective oxidation of the more easily oxidizable niobium pentachloride in the mixture of the pentachlorides so obtained,

The extraction of the mixture so obtained, in which the tantalum is present predominantly or wholly as its pentachoride and the niobium is present predominantly or wholly as its oxychlori'de, is carried out by means of an inert solvent with the exclusion of moisture. As an inert solvent there is to be understood a single solvent or mixture of solvents which is inert towards the chlorides of niobium and tantalum, that is to say, which does not react with these chlorides. As such solvents there may be used either organic or inorganic solvents. As organic solvents there may be mentioned aliphatic or aromatic,

and preferably halogenated compounds, such as bromotanium tetrachloride, silicon tetrachloride, tin tetrachloride, phosphorus trichloride, and especially solvents containing sulfur and oxygen such as thionyl chloride sulfuryl chloride and above all sulfur dioxide.

The extraction may be carried out by treating: the

chlorination mixture in the absence of moisture once or several times with an inert solvent or mixture of inert solvents, and separating the solution containing chiefly the pentachloride from the undissolved substances.

The treatment of the mixture of chlorine compounds of niobium and tantalum with the aforesaid solvents may 'be'carried out in known manner, for example, under atmospheric pressure and at room temperature or at araised temperature, for example, at the boiling point" of the solvent used, batchwise or in a continuous manner. In certain cases it is necessary to work under superatrnospheric pressure. Thus, for example, the mixture may be treatedwith sulfur dioxide at room temperature and under a pressure corresponding to the vapour pressure'of sulfur dioxide, for example, in a mixing or grinding apparatus or continuously on the counter-current principle.

After the extraction, the extracted chloride can be separated from the solvent in known manner, for example, by distilling off the solvent, by precipitation and filtration or by cooling and crystallization, and then the chloride may be further worked up. The insoluble substances may be purified, for'example, by sublimation. The solvent recovered after removing the chloride dissolved therein can of course be used in further extractions.

By the process of this invention mixtures containing niobium and tantalum which are difiicult to split up into theirco'nstituents can be split up into fractions, one of which contains mainly tantalum and the other mainly niobium.

The following examples illustrate the invention, the parts andpercentages being by weight:

EXAMPLE 1 were extracted under a pressure corresponding to the vapour pressure of sulfur dioxide three times with about 30 parts of liquid sulfur dioxide, that is to say, until the extract contained no appreciable amounts of chloride. The three extracts were separately freed from solvent by evaporation.

Analysis" SublimateS Residue R- (1.12 parts) (0.23 part) Percent NbzOa 90. 9 13.0 Percent TazOs 9. 1 87. 0

Thus three fractions were obtained of which two, the extract and the sublimation residue, contain mainly tantalum, and of which the third, the sublimate from the extraction residue, contained mainly niobium.

EXAMPLE 2 sulfur dioxide, the extract on the third occasion containing no appreciable amounts of dissolved substance. The extracts were freed from solvent by evaporation.

The combined extracts, which contained X% (see Table l) of the niobium and tantalum (calculated as oxides) present in the original chlorination product, were analyzed for the ratio of niobium and tantalum (calculated as oxides) contained therein. The combined extracts contained a percent of Nb O and b percent of Ta O (see Table 1).

.The residue insoluble in sulfur dioxide (containing Y+Z percent of the metals present in the original chlorination mixture) were split up by sublimation in vacuo (at 0.1 mm. pressure of mercury) into a sublimation residue R and a sublimate S, and the two fractions were analyzed for niobium and tantalum. The sublimate S, containing Y percent of niobium and tantalum (calculated as oxides) had a content of a percent of Nb O and b percent of Ta O and the sublimation residue R containing Z percent of niobium and tantalum, had a content of a percent of Nb O and 11 percent of Ta O (see Table 1).

TABLE 1 I Extract E Snblimate S Residue R- Percent of Percent of the OhlO- Nb0 T8305 the GhlO- Nbzog T3205 Per- Nbg05 T8105 Temp., O. rination rination cent product product X a b Y a I) Z a t- 47 21 79 41 94 e 12 21 19 46 22 78 39 87 13 15 30 39 26 74 46 87 13 15 8 92 42 22 78 45 89 ll 13 48 18 82 1 Not analyzed.

The first extract, which contained about 90 per-cent EXAMPLE 3 of the extractable material (equal about 1.05 parts), was analyzed for its content of niobium and tantalum. It contained 22.8 percent of niobium and 77.2 percent of tantalum (calculated as Nb O and Ta O respectively).

Theresidue insoluble in sulfur dioxide (about 1.35 parts) was split up by sublimation in vacuo (0.1 mm. pressure of mercury) into a sublimation residue R and a sublimate S, and the two fractions were analyzed for niobium and tantalum.

1 part of a niobium-tantalum mixture, which consisted of about 43 per cent of niobium (calculated as Nb O and about 57 percent of tantalum (calculated as Ta O and'had been finely pulverized with the exclusion of moisture, and which contained the niobium as NbOCl and V the tantalum as TaCl was extracted several times with 5 parts of sulfuryl chloride on each occasion until the extract contained no appreciable quantities of extracted substance (that is to say, extracted seven times with 5 parts of sulfuryl chloride on each occasion). The residue was separated from the solution each time by centrifuging and decanting, and the extracts were freed from sulfuryl chloride by evaporation.

and sulfur dioxide and the resulting solution is separated from the undissolved fraction of the chlorination products.

4. Process according to claim 3 wherein there is used an inert solvent sulfur dioxide maintained in liquid phase The extracts so obtained contained together 60 per 5 by means of a pressure exceeding its vapor pressure at cent (calculated as oxides) of the metalspresent in the working temperature. original mixture, of which 93 percent was tantalum and 7 5. Process for separating niobium and tantalum from percent niobium, and the residue insoluble in sulfuryl one another in materials containing these metals in oxi chloride contained 98 percent of niobium and 2 percent dized form, wherein the material is heated at 400 C. to of tantalum. in 1000 C. in the presence of carbon and chlorine gas, the

EXAMPLE 4 vapors of the chlorination products leaving the chlorina- One partvof amixture of Nbocl and Tacl which had tion zone are rapidly condensed, the condensed mixture been finely pulverized with the gxclusion moisture is treated with liquid sulfur dioxide and the sulfur dioxide was extracted three times with 10 parts of sulfur dioxide Solution cpntaining tantalum pentaqhloride is separated on each occasion. Two further portions of 1 part each of 10 g g msolfuble l f f t 1 f the same mixture were separately extracted, one three recess. or sepaira mg {um an an i times with 5 parts of thionyl chloride on each occasion, 9 another mttenals contzllmilg these metals and the other three times with parts of bromethane on f Wherem the mammal 1s heated at.400 to each occasion. The residues were separated from the 1000 m the pre.senc.e of Carbon and .Chlonne gasithe solutions, by filtration in the case of the extraction with of tha chlqnnatmn products leavmg the m sulfur dioxide and by'centrifuging and decanting in the P Zone 3.1-6 f f i q the condensed i f case of the extractions with thionyl chloride and is treated with liquid sulfur dioxide and the sulfur dioxide methane The extracts were freed from solvent by evap solution containing tantalum pentachloride is separated oration from the insoluble fraction of the mixture, the so-obtained The extracts and the residues were then analyzed for l-Psoluble fraCt 10n and the tantalum Pentachlcrid frao' their contents of niobium and tantalum (calculated as afte? havlflg been freed from the sulfur dloxldle by oxides). The contents of niobium and tantalum in the evaperatlonbfilng each Separately Subllmed for p chloride mixture and also the proportions in the extracts U011 y heatll'lg under feilllced Pressureand residues of the niobium and tantalum (calculated m PI'OCESS fOr Separating niobium and tantalum m as oxides) originally present are given in Table 2. one another, wherein a mixture of tantalum pentachloride TABLE? Composition of Extract Residue the chloride mixture (calcu- Solvent lated as oxides) Percent of Percent of the starting Nbnos, Taro the starting Nb 05, T9405, N0. mixture Percent Percent mixture Percent Percent Nbzos T2105 (calculated (calculated as oxides) as oxides) 43 57 1 55 2. 0 9s. 0 44 so, 53 47 1 47 3.5 96.5 53

42 58 g 3 as 99.5 0.5 1 51 1.5 98.4 (hH Br 55 2 7 50.0 50.0 35 99 1 1 Not analyzed. What is claimed is: and niobium oxychloride is brought into contact with 1. Process for separating niobium and tantalum from anhydrous liquid sulfur dioxide, the resulting solution one another, wherein in a mixture containing tantalum containing tantalum pentachloride is separated from the pentachloride and niobium oxychloride the tantalum insoluble fraction of the mixture and freed from sulfur pentachloride is dissolved in an anhydrous solvent sedioxide by evaporation, both fractions so obtained being lected from the group consisting of thionyl chloride, thereafter sublimed for purification by being heated sulfuryl chloride and sulfur dioxide, and the resulting soseparately under reduced pressure and condensing the lution is separated from the undissolved fraction of the volatilized products. starting mixture.

2. Process according to claim 1, wherein there is used References Clted 111 the file 0f thls P an inert solvent sulfur dioxide maintained in liquid phase 60 UNITED TA PATENTS by means of pressure exceeding to its vapor pressure at working temperature. 3, KrOl June 15, 1948 3. Process for separating niobium and tantalum from FOREIGN PATENTS one another in materials containing these metals in oxi- 5 7 Great Britain June 9, 1939 dlzed form, wherein the material is heated at 400 C. to 1000 C. in the presence of carbon and chlorine gas, the OTHER REFERENCES vapors of the chlorination products leaving the chlorina- I. W. Mellors A Comprehensive Treatise on Inorganic tion zone are allowed to remain at high temperature for and Theoretical Chemistry, vol. 9, 1929 edition, pages at most a few seconds and wherein tantalum penta- 878, 879, 921. Longmans, Green& Co., N. Y. chloride is extracted from the mixture of chlorination Thorpes Dictionary of Applied Chemistry, vol. 3,

products by an anhydrous inorganic solvent selected from the group consisting of thionyl chloride, sulfuryl chloride,

4th edition (1939), page 312, Longmans, Green & Co., N. Y.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 2,842,424 July 8, 1958 Waldemar Sohornstein et a1,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters I Patent should read as corrected below.

Column 1, line 16, for "nioblum" read niobium line 34, for the patent number "2,444,254" read 2,443,254 column 5, line 60, for "en read as line 61, strike out "to"; column 6, line 4, for "an" read .sas Signed and sealed this 24th day of March 1959 (SEAL) Attes t:

KARL H, .AXLINE ROBERT C. WATSON .Attesting Ofiicer Commissioner of Patents 

1. PROCESS FOR SEPARATING NIOBIUM AND TANTALUM FROM ONE ANOTHER, WHEREIN IN A MIXTURE CONTAINING TANTALUM PENTACHLORIDE AND NIOBIUM OXYCHLORIDE THE TANTALUM PENTACHLORIDE IS DISSOLVED IN AN ANHYDROUS SOLVENT SELEKCTED FROM THE GROUP CONSISTING OF THIONYL CHLORIDE, SULFURYL CHLORIDE AND SULFUR DIOXIDE, AND THE RESULTING SOLUTION IS SEPARATED FROM THE UNDISSOLVED FRACTION OF THE STARTING MIXTURE. 